Symmetrical shaded pole electromagnet



Dec. 1, 1970 w. v. DE FOREST E 3,544,936

SYMMETRICAL SHADED POLE ELECTROMAGNET Filed Aug. 2. 1968 F/G3 WESLEY v.DE FOREST MARVIN M. GRAHAM Jaw E 56W ATTORNEYS United States Patent3,544,936 SYMMETRICAL SHADED POLE ELECTROMAGNET Wesley V. De Forest,Long Beach, and Marvin M. Graham, San Pedro, Calif., assignors toRobertshaw Controls Company, Richmond, Va., a corporation of DelawareFiled Aug. 2, 1968, Ser. No. 749,863 Int. Cl. H01f 7/10 U.S. Cl. 335-24510 Claims ABSTRACT OF THE DISCLOSURE An electromagnet having a U-shapedcore comprising a first portion defining a first pole and a secondportion defining second and third poles symmetrically disposed around afourth shaded pole, and an electromagnetic operator comprising theelectromagnet, an electrical winding on the first portion of the coreand a keeper armature disposed on the first pole for fulcrum action andhaving a contact end extending over the second portion of the core tocontact the fourth pole when the winding is energized.

BACKGROUND OF THE INVENTION The present invention pertains to anelectromagnet and particularly to an electromagnet utilizing asymmetrical arrangement of shaded and unshaded poles.

Many attempts have been made to prevent armature bounce and vibration,sometimes referred to as chatter or buzzing, in electromagnetic operatorsystems. The conventional manner in which such vibration is eliminatedis to provide a shaded pole along with a single unshaded pole such thatthe flux sensed by the armature never drops to zero. That is, when thecoil of an electromagnet is energized from an AC. source, the compositeflux from the shaded and unshaded poles is never zero due to the phasedisplacement of the flux at the shaded pole. This use of a shaded polewith an unshaded pole is effective in reducing the vibration obtainedwhen an unshaded pole is utilized by itself; however, this combinationstill provided more vibration than is desirable in the operation ofelectromagnetic switches, valve operators, and other sensitive devices.

Along with their undesirable vibration characteristics conventionalelectromagnets are disadvantageous in that if the shaded and unshadedpoles are laterally spaced there is an unbalanced pull on the armature,and whether the poles are laterally spaced or aligned with thelongitudinal axis of the armature, imbalance exists and is aggravated byvariations in spring bias on the armature and foreign particle depositson the pole faces.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to construct an electromagnet that substantially eliminatesarmature vibrations.

Another object of the present invention is to eliminate vibrations in anelectromagnetic operator by symmetrically disposing a plurality ofunshaded poles around a shaded pole.

A further object of the present invention is to prevent armature bounceand vibration in an electromagnetic operator by constructing theelectromagnet as a four-pole piece with one pole acting as a fulcrum forthe armature.

The present invention has another object in that armature vibrations inan electromagnetic operator are eliminated by disposing a plurality ofunshaded poles sym- "Ice metrically with respect to a shaded pole andthe armature.

The present invention is advantageous over conventional electromagneticoperators in that armature bounce and vibration is substantiallyeliminated to to thereby provide accurate operation of the devices to beoperated upon.

The present invention is generally characterized in that anelectromagnet comprises a first leg defining a first pole, a pluralityof second legs symmetrically disposed around the first leg to define aplurality of second poles, and shading means disposed around the firstleg and an electromagnetic operator comprises the electromagnetdescribed above in combination with an armature disposed so as tocontact another pole of the electromagnet as a fulcrum and extendingover the first and second poles.

Other objects and advantages of the present invention will becomeapparent from the following detailed description of the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in perspective of anelectromagnetic core of the present invention.

FIG. 2 is a front elevational view, partially in section, of anelectromagnetic operator of the present invention.

FIG. 3 is a side elevational view in section of the electromagneticoperator of FIG. 2 in a closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view ofa core 10 of an electromagnet constructed in accordance with the presentinvention. Core 10 is substantially U-shaped and comprises twoupstanding portions, indicated generally as 12 and 14, connectedtogether by a fiat bottom portion 16. Portion 12 defines a pole face 18that extends the entire width of core 10, and portion 14 is separatedinto three legs 20, 22, and 24 each defining a pole face 26, 28, and 30,respectively, with the areas of pole faces 26 and 30 being equal.

Core 10 may be made of any conventional soft magnetic material suitablefor use in electromagnets, and the specific shape of core 10 shown inFIG. 1 is not meant to be limiting in that the important criterion isthat the outside legs of portion 14 be symmetrically spaced from thecenter leg as will be explained hereinafter.

An electromagnetic operator utilizing core 10 is shown in FIG. 2 and issupported by a right angled frame 32, preferably constructed of materialnot susceptible to being magnetized in order to prevent theestablishment of diversionary magnetic fields. Core 10 has a circularrecess 34 adapted to accommodate the flattened head of a protrusion 36which extends from frame 32 through a bore 38 aligned with recess 34 incore 10 in order to secure core 10 to frame 32.

Portion 12 of core 10 has an electrical winding 40 wound therearound,which winding is adapted to be connected to any conventional source ofvarying electrical energy such as an AC. voltage source. Pole 18associated with portion 12 of core 10 acts as a fulcrum for a keeperarmature 42 which is biased at one end by a spring 44 that may beconnected with any stationary structure such as frame 32. Armature 42may be constructed of any conventional easily magnetizable material andis elongated in order to permit contact with pole 28. While armature 42is shown as being planar, it should be noted that armature 42 may haveany shape convenient to the operation of the electromagnetic operator.For instance, if greater movement is required of armature 42 uponenergization of the electromagnetic operator, the spring biased end ofarmature 42 may be extended or the end of armature 42 that contacts pole28 may be offset to require greater movement to cause contact. Armature42 may also be shaped to accommodate the device operated to provide snapaction.

The width of armature 42 is approximately equal to the width of core 10,as can be seen from FIG. 3, and a semispherical bulge or nipple 46 ispressed out at the contact end of armature 42 to provide equalized airgaps between poles 26 and 30 and armature 42 and firm contact with pole28. A leaf spring 48 having an offset end 50 is secured to frame 32 by ascrew 52 such that offset end 50 is in contact with armature 42 directlyabove pole 18 to aid in the fulcrum action thereat. A shading ring 54 isdisposed around leg 22 and may be made of any conventional shadingmaterial such as copper.

With further reference to FIG. 3, which is an elevational sectional viewof portion 14 of core and armature 42 in a closed poisiton, it is seenthat poles 26 and are symmetrically spaced from shaded pole 28, and dueto this symmetry and the configuration of armature 42 the horizontalcomponents of the magnetic fiux at poles 26 and 30 are equal andopposite in their effect on armature 42.

The operation of the electromagnetic operator of the present inventionwill be described with respect to FIGS. 2 and 3 and as operating a valve(not shown). When the electromagnetic operator is in an unenergizedstate, armature 42 is forced away from portion 14 of core 10 by biasspring 44 which may be disposed in tension between a stationary portionof the valve and the operating end of armature 42. The distance betweenarmature 42 and portion 14 of core 10 may be controlled by providing anindependent stop for armature 42, by designing leaf spring 48 to act asa stop due to abutment with armature 42 or by balancing the weight ofarmature 42 with the force of bias spring 44. In any case, in theunenergized state bias spring 44 forces the operating end of armature 42down to, for instance, close the valve.

Upon the energization of coil by an alternating current source forinstance, which energization may be caused by the closing of anelectrical switch either manually or automatically in response to acondition of a system of which the valve is a part, the current throughcoil 40 cause magnetic fiux to be established in core 10. This magneticflux, which is concentrated at poles 18, 26, 28, and 30 magnetizesarmature 42 and pulls the contact end down so that nipple 46 contactsshaded pole 28. The initial downward force on armature 42 is provided byunshaded poles 26 and 30 because shading ring 54 delays the magneticflux concentrated at pole 28. Due to their symmetry with respect toshaded pole 28 and armature 42 and their equal area pole faces, unshadedpoles 26 and 30 prevent lateral movement of armature 42 and reduce thenormal tendency of the armature to bounce or slide on the electromagnet.

The delay or phase displacement of magnetic flux at shaded pole 28caused by shading ring 54 permits armature 42 to be in firm contact withcore 10 throughout each entire cycle of alternating current energizingcoil 40. That is, the phase displacement of magnetic fiux permits fluxto be concentrated at pole 28 when the alternating current is at a Zerolevel.

Variations in spring forces and loads at the end of armature 42 will notadversely affect the operation of the electromagnetic operator of thepresent invention because the symmetry of unshaded poles 26 and 30 withrespect to armature 42 and shaded pole 28 causes armature 42 to besubjected to equal and opposite lateral magnetic forces at all times;and, consequently, any variation of force in the longitudinal directionneed only be overcome by the vertical components of the flux at thepoles of portion 14 of core 10. Vertical bounce of armature 42 is alsoeliminated due to the extension of the contact end of armature 42directly over unshaded poles 26 and 30, and the strong magnetic fieldsat these poles provide firm control of the armature to secure thecontact of nipple 46 with shaded pole 28.

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With respect to operation of a valve, the operating end of armature 42moves up upon energization of the electromagnetic operator to forcenipple 46 to contact pole 28, and the operating end may be connecteddirectly or through mechanical linkage to a valve member to open thevalve.

The shape of the armature to be used with an electromagnetic operatorconstructed in accordance with the present invention, should beconsidered in designing the leg position of the core; however, when thearmature has a longitudinal axis in parallel with the spacing betweenthe two portions of the core and passing through the shaded pole, it issuflicient to dispose the unshaded poles symmetrically with respect tothis axis. The most important criterion in constructing anelectromagnetic operator in accordance with the present invention isthat the shaded and unshaded poles be disposed symmetrically withrespect to each other and to the longitudinal axis of the armature.

The present invention, thus, provides an electromagnetic operator thatmay be used with sensitive devices such as switches and valves andsubstantially eliminates the normal armature vibrations associated withconventional electromagnetic operators.

Inasmuch as the present invention is subject to many variations,modifications and changes in detail, it is intended that all mattercontained in the foregoing description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limiting senseWhat is claimed is:

1. An electromagnetic operator comprising a core having a first portiondefining a first pole and a second portion including first, second andthird legs defining second, third and fourth poles, respectively;

an electrical winding disposed around said first portion of said coreand adapted to be connected to an energization source;

shading means disposed around said first leg of said second portion ofsaid core;

armature means disposed to contact said first pole as a fulcrum andextending over said second portion of said core;

said third and fourth poles being disposed symmetrically about saidsecond pole whereby said armature means may be pulled in withoutvibration when said electrical winding is energized.

2. The invention as recited in claim 1 wherein said armature means has alongitudinal axis, and said third and fourth poles are disposedsymmetrically with respect to said longitudinal axis.

3. The invention as recited in claim 2 wherein said armature means has abulge in the end extending over said second portion for contacting saidsecond pole when said electrical winding is energized.

4. An electromagnetic operator comprising:

a unitary core having a first portion defining a first pole and a secondportion having a plurality of legs defining a plurality of second polesand a third pole;

energizing means coupled with said core;

shading means disposed around one of said plurality of legs; and

armature means disposed so as to be in contact with said first pole andhaving a contact end extending over said second portion of said core andan operating end, said first pole acting as a fulcrum for said armaturemeans;

said second poles being symmetrically disposed around said third polewhereby said armature means may be pulled in without vibration.

5. The invention as defined in claim 4 wherein bias means is connectedwith the operating end of said armature means.

6. The invention as recited in claim '4 wherein said shading means isdisposed around the leg defining said third pole.

7. The invention as recited in claim 4 wherein said cally about saidsecond pole and equidistant from armature means has a longitudinal axis,and said pluralsaid first pole; and ity of second poles are disposedsymmetrically with rea shading ring surrounding said first leg forcausing spect to said longitudinal axis. phase displacement of magneticflux at said second 8. A unitary core for an electromagnet comprising:pole. a first upstanding portion defining a first pole; and o 10. Theinvention as recited in claim 9 wherein an a second upstanding ortionspaced from s id fi t electrical Winding is disposed around said firstupstanding standing portion by a bottom portion and defining PoftiO11for enefgiling Said electl'omagnetsecond, third and fourth poles, saidsecond and third poles being disposed symmetri- 10 References Cltedcally about said fourth pole and equidistant from UNITED STATES PATENTSsaid first pole. 2,162,465 6/1939 Guilder 335-245 9. An electromagnetcomprising: 2,282,065 5/1942 Krautwig 335-244 a generally unitaryU-shaped core having a first up- 2,370,752 3/1945 Ray 335245 standingportion spaced from a second upstanding 15 2,591,773 4/1952 'Blanchet335-276 portion by a bottom portion, said first upstanding 2,736,3432/1956 Douglas et 335245X portion defining a first pole and said secondupstanding portion having first, second and third legs defining second,third and fourth poles, respectively; 20 said third and fourth polesbeing disposed symmetri- 335-281 GEORGE HARRIS, Primary Examiner US. Cl.X.R.

